1. Field of the Invention
The present invention relates to a liquid discharge state detection device that detects a discharge state of a liquid droplet discharged by a recording head, and an image forming apparatus that includes the liquid discharge state detection device.
2. Description of the Related Art
As an image forming apparatus such as a printer, a facsimile machine, a copier, a plotter, a multifunction peripheral that includes the respective functions thereof or the like, an inkjet recording apparatus or the like is known as an image forming apparatus of a liquid discharge recording type using a recording head that discharges a liquid droplet, for example.
Such an image forming apparatus of a liquid discharge recording type discharges an ink droplet to a recording medium from a recording head, and forms an image (“records”, “prints” or the like being also used for the same meaning) on the recording medium. There are two categories of image forming apparatuses of this type, i.e., serial-type image forming apparatuses and line-type image forming apparatuses. In a serial-type image forming apparatus, a recording head discharges ink droplets and forms an image while moving in a main scan direction. In a line-type image forming apparatus, a line-type recording head is used, and the line-type recording discharges ink droplets and forms an image while not moving.
In embodiments, examples of an “image forming apparatuses” of the liquid discharge recording type include apparatuses that cause ink droplets to reach recording media such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics and so forth. “Forming an image” means not only giving an image having the meaning such as characters/letters, a figure, or the like, to a recording medium, but also giving an image having no meaning such as a pattern or the like to a recording medium (merely causing ink droplets to reach a recording medium).
Further, “ink” is not limited to those commonly referred to as ink, and will be used as a general term of all the liquids with which an image can be formed such as those called a recording liquid, a fixing liquid, a resin, a liquid and so forth. An “image” is not limited to a planar one, and examples thereof include an image given to an object that has a three-dimensional shape and a three-dimensional image itself obtained from three-dimensionally shaping a thing.
In such an image forming apparatus, an image quality may be degraded when a problem occurs in discharging ink from a recording head due to an increase in ink viscosity caused by evaporation of a solvent from nozzles, ink droplets being solidified, adhering of dust/dirt, ink getting mixed with air bubbles, and/or the like, since the recording head discharges ink droplets to a recording medium from the nozzles and carries out recording.
In this regard, liquid discharge state detection devices have been known which detect states of liquid being discharged from recording heads. Such liquid discharge state detection devices include one of a direct light type in which a light beam is emitted along a row of nozzles from one side of the row of nozzles of a recording head, a light reception unit is placed which directly receives the light beam at the other side, and thus, it is detected whether liquid is being discharged (see Japanese Laid-Open Patent Application No. 2007-118264 (Patent reference No. 1), for example). Another one is a device of a forward scattered light type in which a light beam is emitted along a row of nozzles from one side of the row of nozzles of a recording head, a light reception unit is placed at a position shifted from the optical axis of the light beam which receives scattered light reflected by a liquid droplet, and thus, it is detected whether liquid is being discharged (see Japanese Laid-Open Patent Application No. 2009-113225 (Patent reference No. 2), and Japanese Laid-Open Patent Application No. 2009-132025 (Patent reference No. 3), for example).
However, in the above-mentioned liquid discharge state detection device of the forward scattered light type of the Patent references No. 2 or 3, the light receiving unit may be affected by reflected light from the recording medium, the recording head or the like or disturbance light (referred to as “noise light”), the signal to noise ratio (SN ratio) between the received light amount of the noise light in the light reception unit and the received light amount of the above-mentioned scattered light in the light reception unit may be degraded, and thus, it may not be possible to detect the state of liquid being discharged from the recording head.